An internal combustion engine system is typically equipped with a cooling subsystem that basically circulates liquid coolant between coolant passages in an engine and a heat exchanger located remotely from the engine. The coolant absorbs heat produced by the engine and is carried to the heat exchanger, which dissipates the heat from the coolant into the air. A conventional cooling subsystem also typically includes one or more pumps, filters, thermostats and other valves, and conduit interconnecting such devices. Conventional cooling subsystems also usually include static temperature sensors that monitor static coolant temperature to diagnose thermostat valve failures.